Diets for RearingScyphophorus acupunctatus(Coleoptera: Curculionidae)

Abstract

The weevil, Scyphophorus acupunctatus Gyl lenhall, is a pest of several species of economically important century plants, Agave spp. (Asparga les: Asparagaceae), and of Mexican tuberose, Po lianthes tuberosa L. (Aspargales: Asparagaceae). Larvae feed in the tuberose bulb, and damage 35 to 69% of the crop (Camino et al. 2002). In the field, Hernandez (2003) observed that S. acu punctatus larvae feeding on tuberose bulbs form a series of galleries or tunnels and complete their development within a cocoon from which the adult emerges. Copulation is carried out among the bulbs, where the female lays her eggs. Due to the economic importance of S. acupunc tatus, the scarcity of information on its biology, and the urgent need to accelerate both basic and applied research, it is essential to develop meridic diets for immature stages as alternatives to the natural diet. Meridic diets for insects confer a basic advan tage over the seasonally available natural nour ishment, since they make possible continuous rearing to support laboratory bioassays for the study of their ecology, physiology, and behavior (Singh 1983). Contamination of rearing media by microorganisms is a major issue that must be resolved when attempting to develop an artificial diet adequate for rearing an insect culture under laboratory conditions. To this end, antimicrobial agents are used, such as formaldehyde, methyl P hydroxybenzoate, sorbic acid, and certain antibi otics such as penicillin, streptomycin, and aureo mycin (Singh 1976). These constituents are not always innocuous, because they can be directly toxic to insects, and because they can affect es sential microbial symbionts (Dunkel et al. 1982). A compound's safety level can be defined as the concentration that does not reduce the yield of pu pae and that does not prolong the period of larval development more than 25% of the control (Singh & House 1970). Above this safety level, antimicro bial agents produce toxic effects in proportion to the concentration utilized; and the most frequent toxic effects are reduction of the insect's size, pro longation of the larval period, and the increase in mortality of the larval and pupal stages (Bass & Barnes 1969; Singh & House 1970; Dunkel& Read 1991). The purpose of this study was to develop a me ridic diet for mass rearing of S. acupunctatus in the laboratory that would supply the nutritional requirements of development, fecundity, and fer tility of the insect; and that could facilitate the reliable production of larval stages needed to con duct studies of their biology, and behavior; and to obtain other information basic to achieving effec tive management of this pest. In a tuberose plantation located in the Emil iano Zapata municipality, Morelos, Mexico, we collected damaged tuberose bulbs, from which we obtained S. acupunctatus larvae of different stages, which we separated in the laboratory and placed individually in 100-mL plastic containers each with a tuberose-bulb and moistened paper filter. Next the containers were placed in a Preci sion® model 818 incubator at 27 ± 1 °C, 60-70% RH, and 12:12 h L:D until the emergence of the adults. We placed sets of 40 pairs of the emerged adults in 5.8 x 2.7 cm plastic containers each with perforations in the container top to promote air circulation and to help avoid the growth of fungi; 20 g of the tuberose bulb was placed within each container for feeding and oviposition. This tube rose was replaced every 3 d, and with the aid of a Nikon stereoscopic microscope, part of the epi dermis was removed to expose the eggs. The eggs were removed with a no. 1 marten hair brush and deposited in 15 x60 mm petri dishes with wet fil ter paper and stored in the incubator until eclo sion.